Harmonograph

just the two singleaxis pendulums. This can be done by mounting two brackets on the table near the rotary pendulum with holes to take a long horizontal bolt slightly to one side to which the shaft can be clamped. Pens should be fine, light and freeflowing. Most stationers and shops selling draughtsmens and artists materials offer a variety avoid ball or thick fibre pens. For best results use shiny art or imitation art paper, ordinary copypaper for preliminary experiments. If the pen is left on the paper to the end there is usually an unsightly blob. To avoid this, mount a short pillar on the table with an adjustable lever carrying a piece of thin dowel placed under the pen arm. By raising the dowel gently the pen is lifted off the paper without jogging it. This device should also be used before the pen is lowered to the paper. By watching the pen you can see what pattern is being made, and nudge it one way or the other by pressure on the pendulums. For ratios outside the octave, such as 41, you may need to try another harmonograph such as Goolds twinelliptic pendulum left. builDing a harmonograPh